Digital subscriber line (DSL) technologies provide potentially large bandwidth for digital communication over existing telephone subscriber lines. The DSL technologies were designed in a way that they could peacefully coexist with the standard POTS (Plain Old Telephone Service) frequency spectrum. The two services can coexist because the DSL spectrum only uses frequencies above the POTS spectrum. The POTS spectrum ranges from frequency levels near that of direct current (DC) to approximately 4 kHz. The ADSL (Asymmetric DSL) frequency spectrum starts above the POTS spectrum and extends up to approximately 1.1 MHz. A frequency guard band is placed between the POTS spectrum and the ADSL spectrum to help avoid interference. The lower-frequency part of the ADSL spectrum is for upstream transmission (i.e., from the customer to the central office) and the upper-frequency part of the ADSL spectrum is for downstream transmission (i.e., from the central office to the customer).
In particular, ADSL can be adjusted to the characteristics of the subscriber line by using the so-called discrete multi-tone (DMT) technique. The DMT technique employs frequency division multiplexing by dividing the bandwidth of a twisted pair into a number of frequency carriers or sub-carriers which are called tones. The frequency carriers or sub-carriers are mostly spaced at 4.3125 kHz intervals, with 224 of the carriers or sub-carriers used for the downstream data in the range from 138 kHz to 1.1 MHz and 25 of the carriers or sub-carriers used for the upstream data in the range from 26 kHz to 133 kHz in case of frequency division duplexing.
Among the ADSL technologies, new technologies called “Very High Bit Rate DSL” (VDSL) have been developed. Meanwhile a new standard, namely the VDSL2 (G.993.2) standard, was approved by the International Telecommunication Union-Telecommunication (ITU-T) Section in May 2006. The VDSL2 standard is designed to increase both data rate and physical reach over the copper network, achieving data rates in excess of 25 Mbps over long loops (4-6 kft) and symmetrical data rates of 100 Mbps over short loops (less than 1 kft). The VDSL2 standard includes many of the features and functionalities contained in the former Asymmetric Digital Subscriber Line 2 (ADSL2+) standard, including advanced diagnostics, a common management interface and the ability to maximize the use of bandwidth and bit rate, making it an ideal access technology for delivering video.
The VDSL2 standard is a very complex standard supporting a wide range of capabilities and settings. To reduce the complexity of using VDSL2 and confronting the wide range of settings, VDSL2 supports “profiles” that represent subsets of the full range of settings, with each of the profiles being directed to addressing different deployment contexts. The profiles correspond to various band plans and specify numerous parameters ranging from geographic-specific requirements to variations of reach and bandwidth. In particular, the VDSL2 standard defines a wide range of settings for various parameters that could potentially be supported by a VDSL2 transceiver. Profiles are specified to allow transceivers to support a subset of the allowed settings and still be compliant with the protocol standard. The specification of multiple profiles allows vendors to reduce implementation complexity and develop implementations that target specific service requirements.